This invention relates to shock absorbers, and, more particularly to velocity responsive fluid actuated friction dampers. The friction dampers of the present invention are useful for a wide range of friction damping applications but are intended principally for use in land vehicle suspension systems.
In U.S. Pat. No. 4,979,595, issued to the present inventor on Dec. 25, 1990, embodiments of a fluid actuated friction damper are disclosed in which relative movement between inner and outer telescopic bodies is damped by friction shoes on the inner body expanded by fluid pressure into engagement with a continuous internal surface on the outer body. In certain of the disclosed friction damper embodiments, an external dual pressure source is used to expand a single set of friction shoes under one pressure during one direction of relative inner and outer body movement and under a different pressure in the other direction of such relative movement. In other embodiments disclosed, a single external pressure source is applied alternately to axially spaced sets of friction shoes of differing effective area. Thus, in one direction of relative inner and outer body movement, the single fluid pressure is applied to one of the two sets of friction shoes whereas in the other direction of such relative movement, the same pressure is applied to the other of the two sets of shoes.
From the different embodiments disclosed in the prior patent, it is apparent that in one case, the friction force is changed upon directional reversal of body movement, while in the other case, the effective friction area is changed on directional reversal. In both cases, the relative direction of inner and outer body movement must be sensed, a controller is required to respond to the sensed direction of relative movement, and either the pressure of the fluid is required to be changed, as in the case of a dual pressure source, or the fluid flow path between the external source of fluid pressure is required to be changed, with each sensed direction of body movement reversal.
While the operational principles of the friction damper embodiments disclosed in the aforementioned patent are sound, the external pressurized fluid system is relatively complicated, and as such, costly from the standpoints of manufacture, installation and maintenance. As a result, the benefits of the controlled fluid pressure actuated friction damper represented by the embodiments disclosed in the prior patent have not been realized in a commercially competitive shock absorber market.